The invention relates to the use of at least one sophorolipid in the lactone form, as an agent for stimulating the metabolism of skin dermis fibroblast cells.
The invention is of particular application to the fields of cosmetology and dermatology.
Sophorolipids are glycolipids; they are produced by fermentation using Candida or Torulopsis type yeasts such as Torulopsis magnoliae, Candida bombicola, Candida apicola or Candida bogoriensis. 
The constituent glucide in extracellular sophorolipids is sophorose (2-O-xcex2-D-glucopyranosyl-xcex2-D-glucopyranose). That sugar can be acetylated in the 6xe2x80x2 and 6xe2x80x3 position and is bonded to a fatty hydroxyacid in the xcfx89 or xcfx89xe2x88x921 position via an acetal bond.
The lipid fraction of sophorolipids is composed of a plurality of fatty hydroxyacids which differ in their chain length, in the number and position of the unsaturated bonds, and in the hydroxylation position. For each of these hydroxyacids, there are different structural forms which differ from each other by a lactonisation (or not) of sophorose (principally in the 4xe2x80x3 position) or by an acetylation (or not) in the 6xe2x80x2 or 6xe2x80x3 positions.
The mixtures of lipid sophoroses produced by fermentation can be resolved and analysed by high performance liquid chromatography using a water-acetonitrile elution gradient. About twenty individual compounds have been observed.
In their unrefined form, sophorolipids are constituted by a mixture of at least one sophorolipid in the lactone form and at least one sophorolipid in the acid form.
The respective contributions of each of the constituent hydroxyacids determined by gas chromatography for the different classes of sophorolipids and the distribution of these classes are shown below. The most abundant fatty hydroxyacid constituent, for example, is 17-hydroxyoctadecenoic acid (17-hydroxyoleic acid).
The properties of the unrefined sophorolipids and sophorolipids in the acid form which are relevant to countering cutaneous ageing, namely their action as an anti-radical and anti-elastase protective agent and their repairing, restructuring and firming action, have been described in International patent application WO 95/34282 and French patent application FR 96/16093 respectively.
Further, prior art is illustrated in European patent EP-A-0 209 783, FR-A-2 735 979 and EP-A-0 850 the latter of which describes the use of sophorolipids in the unrefined or acid form as an agent for stimulating the metabolism of dermal fibroblasts.
Properties pertaining to stimulation of the metabolism of skin fibroblasts by the lactone fraction of the sophorolipids, isolated and purified from the mixture obtained from fermentation, have not been described. This constitutes the subject matter of the invention.
The mechanical properties of the skin are primarily due to collagen fibres which constitute the principal framework of the dermal matrix.
Collagens are constituted by a family of about twenty distinct proteins, half of which are represented in the dermis. They are proteins which are rich in proline and hydroxyproline and are synthesised by fibroblasts.
On ageing, the metabolism and/or structure of the collagens can be modified. A reduction in collagen synthesis and an increase in fibre cross-linking is observed. Further, during cutaneous ageing, cell renewal is slowed down.
Unrefined sophorolipids obtained by fermentation using the process described in EP-B-0 516 803 have a beneficial action on the synthesis of collagens by dermal fibroblasts, as described in the Applicant""s patent application FR 96/16093.
The lactone fraction of sophorolipids has been isolated and purified from a sophorolipid mixture obtained after fermentation.
Purification is carried out by precipitation and crystallisation from ethanol using a protocol described, inter alia, by A. P. Tulloch et al., (Can. J. Chem. 40, 1326 (1962)).
At the end of the purification process, the lactone fraction obtained is a white solid. Thin layer chromatographic analysis shows that the product is generally composed of 95% of sophorolipids in the lactone form, the majority of which are in the diacetylated lactone form.
It has been shown that this lactone fraction of the sophorolipids comprising diacetylated lactones as the major portion could be effectively used as an agent for stimulating the metabolism of skin dermis fibroblast cells.
The lactone fraction can preferably comprise at least 70% by weight of diacetylated lactones, more particularly at least 80% by weight. It is obtained by dissolving the unrefined sophorolipids in ethanol, crystallising then filtering and re-crystallising from ethanol followed by filtering. The recovered product is washed then dried.
A lactone fraction comprising a mixture of sophorolipid lactones with the formula given below is preferably used, in which formula R is an acetyl group, and where R1 is a hydrogen atom or an alkyl group containing 1 to 9 carbon atoms when R2 represents a chain containing 7 to 16 carbon atoms, or R1 is hydrogen or a methyl group when R2 represents a saturated or unsaturated hydrocarbon chain containing 12 to 17 carbon atoms. 
The purified sophorolipid fraction in the mainly diacetylated lactone form is active as a re-structuring, agent and connective tissue repairing agent and thus acts against cutaneous ageing. More precisely, it stimulates collagen neosynthesis in vitro, advantageously more than the unrefined sophorolipid mixture obtained on fermentation.
The purified sophorolipid fraction can be used in concentration ranges or 0.01 ppm to 5% (w/w) of dry matter in the formulation and in particular in water/oil emulsions, oil/water emulsions, gels, serums, lotions or shampoos.
More particularly, it is used in concentration ranges of 50 ppm to 1% (w/w) of dry matter.
The purified lactone fraction can be used alone in the formulation or it can be associated with the unrefined sophorolipid mixture obtained after fermentation where the pH is in the range 3 to 7.5, or it can be associated with deacetylated acid sophorolipids prepared in accordance with FR 96/16093, protonated and/or in the acid form, at least partially in the form of monovalent or divalent metal salts.
The deacetylated acid sophorolipids can also be used in a derivative form, for example in the form of an ester. In this case, their fatty acid function is at least partially esterified by reaction with a linear or branched alcohol containing 1 to 18 carbon atoms, preferably 1 to 8 carbon atoms. The esters can also be associated with the purified sophorolipid fraction described in the present application.
When associated with the purified lactone fraction of the invention, the unrefined sophorolipids can be used in a concentration of 0.01 ppm to 10% (w/w) of dry matter, more particularly 80 ppm to 2% (w/w) of dry matter.
When in the acid form or in the form of a derivative, they can be used in a concentration of 1 ppm to 10% (w/w) of dry matter, preferably 0.02% to 1% of dry matter.
As regards skin re-structuring, repair and protection, it may be of interest to associate in a formulation the purified lactone fraction, which may or may not already have been mixed with the sophorolipids as mentioned above, with ascorbic acid for its dermal re-structuring properties, with vitamin E and its esters, for its active role in anti-radical protection, and/or with vitamin A and its esters, in particular retinyl palmitate, to improve repair of the connective tissue and the epidermis during actinic ageing, inter alia.
It may also be advantageous to combine the purified lactone fraction which may or may not be mixed with other sophorolipids, with alpha or beta hydroxyacids containing 2 to 7 carbon atoms (lactic acid, malic acid, tartaric acid, glycolic acid, citric acid, iso-citric acid, salicylic acid . . . ) which may or may not be in the form of their salts, and their esters, the beneficial role of which has been extensively described in connection with epidermis renewal.